Photodynamic Therapy

Photodynamic therapy (PDT) provides semi-selective tissue destruction and a general antimicrobial effect. It is currently used extensively for the treatment of precancerous lesions or non-melanoma skin cancer [2]. The treatment is based on the activation of a photosensitizer applied to the tissue (usually absorbed through the skin surface), and subsequent tissue destruction. The photosensitizer most commonly used at the time of writing is either aminolevulinic acid (ALA, 20% cream) or esterified aminolevulinic acid. Other photosensitizers are available for intravesical therapy, for example, but their effects on skin diseases are as yet unproven. Similarly, potential photosensitizers, such as methylene blue, are limited in their effects to being antimicrobial. ALA can be purchased from a supplier of analytic substances, or bought as one of two commercially available products (Metvix®, Photocure, Norway or Levulan®, Dusa Pharmaceuicals, USA).

It has been shown that ALA penetrates the skin and is absorbed, theoretically allowing it to reach superficial lesions of HS. Following absorption of the substance it is metabolized along the heme pathway to protoporphyrin IX, which

Table 24.1. Experimental physical therapies in hidradenitis suppurativa (HS)

Treat- Patients Location Treatment Follow- Effect Complications Refer ment up ence

Table 24.1. Experimental physical therapies in hidradenitis suppurativa (HS)

Treat- Patients Location Treatment Follow- Effect Complications Refer ment up ence

1

PDT

Four

One axillary,

20% 5-ALA

3 months

Three

None

[S]

women,

one axillary

for 15-30 min,

patients:

aged

and inguinal

followed by blue

75% im-

19-46

areas, two in-

light, 1- to

provement;

years

guinal areas

2-week intervals;

one patient:

three to four

100% im-

treatments

provement

2

PDT

Four

Three axillary

20% 5-ALA

8 weeks

No

One dropout be-

[6]

patients

disease, one

for 4 h, followed

significant

cause of discom-

groin disease

by 533 nm laser

improvement

fort,

or 570-670 nm

one experienced

broad band light

worsening

giving 15 J/cm2

once weekly

for 3 weeks

S

Cryo

Ten

Three axillary,

Cryotherapy

Not

Four

Average healing

[1S]

therapy

women,

one breast,

using liquid

stated

marked im-

time 25 days,

aged

four groin,

nitrogen to freeze

clearly,

provement,

6/10 experienced

24-45

one axillary

single nodules

but ap-

four im-

postoperative

years

and groin,

to a core temper-

parently

provement,

infection,

one all three

ature of -20 °C

up to

two no

two experienced

sites

6 weeks

response

ulceration,

(end of

three graded

healing)

pain during heal-

ing as maximum

on a 1-4 score

is a potent photosensitizer. The process occurs naturally as the main pathogenic process in porphyria. In healthy tissue the protoporphyrin IX is further metabolized by the enzyme fer-rochelatase to non-phototoxic substances. In metaplastic or neoplastic tissue the activity of ferrochelatase is lower than that in healthy tissue, and a semi-selective accumulation of photosensitizer therefore occurs, which allows more targeted destruction of the metaplastic or neo-plastic tissue.

PDT has recently been tested in a number of non-neoplastic diseases. These include acne rosacea [3], acne vulgaris [4] and HS [5, 6] (see Table 24.1). For HS two studies have been published. The first study, by Gold et al. [5], describes four cases treated with PDT (Levulan and blue light). Only a short incubation period was used, and the treatment was repeated three to four times. No co-morbidity was reported, and at follow-up 3 months afterwards all cases had improved 75-100%, suggesting that the treatment may be of benefit. The exact outcome variables were not stated, e.g., VAS scores or Sartorius scores. The study is interesting but not well documented, and the inclusion criteria open the possibility that simple furunculosis rather than HS was treated. In a subsequent series of cases Strauss et al. [6] described four patients treated with generic 20% ALA and either 633 nm laser or a 570-670 nm broad band light source without significant effect. A longer incubation time and better case definition were used. Furthermore the use of red light allows deeper penetration of the light energy and therefore this is theoretically more suitable for the treatment of HS. The author's limited experience is in better accordance with the latter report than with the former. For HS the lesions treated most successfully have apparently been those of

Stage I disease, suggesting that sinus tracts are not affected and that either the inflammatory process itself or pro-inflammatory substances are targeted.

The mechanisms by which PDT affects these diseases is not known, but it has been suggested to be via tissue destruction of, for example, hy-perplastic infundibular epithelium in acne, or by a simple antibacterial effect analogous to the use of blue light in acne. Additional practical problems are however involved in the use of PDT for HS. It is well established that up to one-third of all PDT patients experience considerable pain during illumination. In the study by Strauss et al. [6] one of four patients dropped out due to pain and discomfort. This appears to be particularly associated with larger areas being treated, and with the sensitivity of the areas, e.g., it is usually worse on the nose than on the back. Even if PDT is found to be effective, this factor may prove to be significantly restrictive for the use of PDT in HS.

The discrepancy between the results observed strongly suggests the need for a controlled trial, and may be due to the stringency of inclusion criteria, variation in the stage of HS being treated, and a number of other factors.

How To Prevent Skin Cancer

How To Prevent Skin Cancer

Complete Guide to Preventing Skin Cancer. We all know enough to fear the name, just as we do the words tumor and malignant. But apart from that, most of us know very little at all about cancer, especially skin cancer in itself. If I were to ask you to tell me about skin cancer right now, what would you say? Apart from the fact that its a cancer on the skin, that is.

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